With experiments with volume controls go back as far as the 1970's, this is what has bought about the ldr Lightspeed Attenuator.
Almost all rotary switches have a stiff disc wiper made out of a different material to the springier metal that the leaf/leaves are made out of.The two contact points in relays are at least made out of the same material.
It is comon knowledge that two different metals that are a touch contact with current/voltage passing through them will creat a "diode effect" electrolosis or glavaic.
Herve Delartz of DartZeel backs this up as well, this is why he does not use contact volume controls either in his $25k NHB-18NS preamp but uses ldr's which have no contact.
http://www.6moons.com/audioreviews/dartzeel2/preamp.html
Quote interview with Herve:
Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light. However, until all the patents are in place, I would prefer not to specify the details.
Cheers George |
I believe that the volume potentiometer (pot) is the single most important component that can have detrmental effect on sound quality, this is why they all sound different to each other.
All volume controls have pin point touch contact that are purposely made light in pressure as not to wear out the resistive track or contact points, all the music signal has to try to pass through these contacts.
These contacts/track are also mostly made dissimilar elements/metals which can have a "diode effect" which tries to rectify the ac music signal, this is a form of distortion.
In order what I believe is the best type of volume controls.
1: Lightspeed (ldr based) Attenuator or TVC (transformer based) = no contacts in the siganl path.
2: Mercury Wetted Relays = with gold or silver contacts in a mercury bath, they also resist tranishing /arcing, also are becoming illegal.
3: Good quality relays = with gold or silver contacts
4: Switched resistor = double leaf, each side of the wiper contact
5: Switched resistor = single leaf on one side of the wiper
6: Potentiometer (Pot) = conductive plastic track
7: Potentiometer (Pot) = carbon track
Cheers George |
Hi Lacee, I tried to look at a pic of the Acoustat servo tube OTL amps, and it looks to have passive volume controls on the input to them, if so, if you or someone can remove them from the circuit (not just bypassed) then the Lightspeed Attenuator will jump up another order of SQ magnitude for you again.
Cheers George |
Here is a good article for those who are interested to see how much their active preamp or passive volume control, is adding colourations/distortions to their sound.
It's called the "Ravel's Bolero Test" and you need a CD or LP of it or like it to conduct the test.
http://www.high-endaudio.com/RC-Linestages.html click on Bolero Test, scroll down to "CD Player?" if you have a cd player
It is basically doing what I suggest you do 2 posts back
Cheers George |
He was talking about how the volume control has changed the sound. And I say given the same value they all sound different to each other. I believe because of materials used and contact point pressure, given the same value they are the single most worst component that can change the sound in equipment. They are fundamentally flawed. It's just like having loose/dirty rca plugs/sockets if you clean them with contact cleaner (plug and socket) you will hear a massive difference to your sound, and these have ten/hundred times the contact area than the miniscule area a pot has.
Cheers George |
The oringal question was not so much about his Dynaco preamp for showing up the differences in volume control sounds, which will be magnified to a larger extent with higher rez amps.
But the reasons why they sound different! And why he was not imagining things.
Cheers George |
No but it's what all and I mean all audio desigers use, it's a good indication of if what your looking/measuring at is as close to a "piece of wire" nothing added or taken away, and all designers use these non musical wave forms to see what's going on.
No I don't do kits but here I show all how to build one themselves.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html
Cheers George |
Yes you are right with these TVC's as well, they do also have inductances, have you ever seen what happens to 20khz square wave through them, they can either ring their brains out or be severly bandwidth limited. What goes in doesn't come out unscathed in nearly all ones I have tested on the bench.
Cheers George |
Inductive?? the worst you can have is an iductive wire wound pot, that comes in at no.8 on my decending horror list?
Cheers George |
He asked "Am i imagining things?" I say no he's not and give him the reasons that's all.
And I'm not saying the Lightspeed Attenuator is the answer, even it doesn't quite sound as good as going direct. In fact I've said many times if you want to hear the truth of what the source is giving, then listen to your source directly pluged into the poweramp with a very quite cd. Then listen at the same level with a pre (active or passive) in the way at the same level, then go with the one that sounds closest to the direct sound. Because this is the one that is least imprinting (colouration/distortion) it's own signature onto the music signal compared to the direct sound, and therefore is the closest to the most transparent sounding eg: (a piece of wire with or without gain)
Cheers George |
